1. Field of the Invention
The invention relates to the transfer of electric energy to a vehicle, in particular to a track bound vehicle such as a light rail vehicle (e.g. a tram) or to a road automobile such as a bus.
2. Description of Related Art
The invention also relates to a corresponding method of manufacturing the system and to a corresponding method of operating the system.
Track bound vehicles, such as conventional rail vehicles, mono-rail vehicles, trolley busses and vehicles which are guided on a track by other means, such as other mechanical means, magnetic means, electronic means and/or optical means, require electric energy for propulsion on the track and for operating auxiliary systems, which do not produce traction of the vehicle. Such auxiliary systems are, for example, lighting systems, heating and/or air condition system, the air ventilation and passenger information systems. However, more particularly speaking, the present invention is related to a system for transferring electric energy to a vehicle which is not necessarily (but preferably) a track bound vehicle. A vehicle other than a track bound vehicle is a bus, for example. An application area of the invention is the transfer of energy to vehicles for public transport. However, it is also possible to transfer energy to private automobiles using the system of the present invention. Generally speaking, the vehicle may be, for example, a vehicle having an electrically operated propulsion motor. The vehicle may also be a vehicle having a hybrid propulsion system, e.g. a system which can be operated by electric energy or by other energy, such as electrochemically stored energy or fuel (e.g. natural gas, gasoline or petrol).
In order to reduce or avoid electromagnetic fields where no vehicle is driving at a time, segments of the conductor arrangement may be operated where required only. For example, the lengths of the segments along the path of travel are shorter than the length of a vehicle in the travel direction and the segments may be operated only if a vehicle is already occupying the respective region of the path of travel along which the segment extends. In particular, occupied by a rail vehicle means that the vehicle is driving on the rails along which the segment extends. For continuous energy transfer while the vehicle is driving, it is proposed that the segment is switched on (i.e. the assigned controller starts the production of the alternating current through the segment) before a receiving device of a vehicle for receiving the transferred energy enters the region of the path of travel along which the segment extends. However, this means that two or more than two consecutive segments may be operated at the same time. Otherwise, the energy transfer to the vehicle may be interrupted and transients of the voltage induced in the vehicle's receiver may be generated.
WO 2010/031593 A1 describes a system and a method for transferring electric energy to a vehicle, wherein the system comprises the features mentioned above. However, the segments are electrically connected in series to each other and there is one inverter at each interface between two consecutive segments. It is disclosed that switches of the inverters are controlled to produce the alternating current. Each switch may be controlled by a drive unit which controls the timing of individual processes of switching on and switching off the switch. The drive units may be controlled by a controller of the inverter which coordinates the timing of all drive units. The synchronization of different inverters may be performed by a single higher-level control device by transferring synchronization signals to each controller of the inverters to be synchronized. A synchronization link may be provided, which may be a digital data bus. The link extends along the path of travel of the vehicle and comprises connections to each controller in order to transfer synchronization signals. In addition, there is also a connection from each controller to the synchronization link. The reverse connections are used to transfer signals from the controllers to the synchronization link and thereby to other controllers which are connected to the synchronization link. One of the controllers being a master controller at a time outputs synchronization signals via the reverse connection and via the synchronization link to the other controllers for synchronizing the operation of all controllers which are operated at a time. If the inverter which is controlled by the master controller ceases operation another controller takes over the task of being the master controller. The new master controller outputs synchronization signals via its reverse connection and via the synchronization link to the other controllers.
According to WO 2010/031593 A1, synchronization is performed either at a phase shift or with no phase shift. This means that at opposite ends of one segment or of consecutive segments inverters are either operated with phase shift or no phase shift and, correspondingly, an alternating current flows through the phase lines of the segment or consecutive segments, if there is a phase shift, or no current flows through the phase lines, if there is no phase shift. As a result, the synchronization disclosed in WO 2010/031593 A1 is performed for the sole purpose to either generate an alternating current or not to generate an alternating current in a segment or in consecutive segments.
It is a disadvantage of this conductor arrangement having consecutive segments which are connected in series to each other that there is still an electric voltage between the alternating current phase lines of the segments and a reference potential if the alternating current carried by the phase lines of the segments is zero. Consequently, it is more difficult to meet requirements concerning electromagnetic compatibility (EMC). Furthermore, the phase shift between inverters at opposite ends of a segment or of consecutive segments may not be exactly zero. As a result, electric currents may flow through the phase lines of the segment(s) unintentionally.